Roll control system for a motor vehicle

ABSTRACT

( 57 ) A roll control system ( 20 ) for installation between axially aligned wheels of a motor vehicle, the roll control system comprising a torsion bar ( 22 ); a damper ( 24 ) attached to one end ( 28 ) of the torsion bar and attachable to one of the wheels; and attachment means ( 25 ) attached to the other end ( 29 ) of the torsion bar and attachable to the other wheel; wherein the damper comprises an axially extending cylindrical housing ( 52 ); a piston ( 34 ) slidably mounted inside the housing; a piston rod ( 58 ) connected to the piston, extending out of one end ( 55 ) of the housing, and movable in an axial direction relative to the housing; a floating piston ( 35 ) slidably mounted in the housing between the piston and the other end of the housing; a compensation chamber ( 37 ) between the floating piston and the other end ( 54 ) of the housing containing a first pressurised fluid; a compression chamber ( 30 ) between the floating piston and the piston containing a second pressurised fluid; a rebound chamber ( 32 ) between the piston and the one end of the housing containing the second pressurised fluid; valve means ( 36 ) on the piston allowing restricted flow of the second pressurised fluid between the compression chamber and the rebound chamber; a rebound stop ( 60 ) positioned in the rebound chamber between the piston and the one end of the housing and providing a spring-effect on the movement of the piston towards the one end of the housing; and a compression stop ( 62 ) providing a spring-effect on the movement of the piston towards the floating piston. Provides an improved passive roll controle system.

TECHNICAL FIELD

[0001] The present invention relates to a roll control system for amotor vehicle, and in particular to a passive or semi-active rollcontrol system.

BACKGROUND OF THE INVENTION

[0002] In order to prevent excessive rolling (which has an impact onvehicle attitude and handling) of a motor vehicle, especially duringcornering, it is known to provide a passive roll control systemcomprising a torsion bar between the front wheels of a motor vehicle,and, in some cases, a second torsion bar between the rear wheels.However, during straight line motion of a vehicle and when the vehicleis off-road, the torsion bar can have a detrimental effect on comfortand wheel articulation because the torsion bar provides solely a springeffect. Semi-active roll control systems have been proposed whichmonitor various vehicle conditions. Such roll control systems include alocking device associated with the torsion bar and the wheels. When thesensed vehicle conditions indicate roll stiffness is not required, thelocking device is unlatched to effectively disconnect the effect of thetorsion bar between the wheels. When the sensed vehicle conditionsindicate that roll stiffness is required, the locking device is latchedto connect the wheels by way of the torsion bar. EP-A-0829383 describesa roll control system having a latch/de-latch arrangement.

SUMMARY OF THE INVENTION

[0003] The object of the present invention is to provide an improvementto the known passive roll control systems, and, if required, adapt thepassive system to provide a semi-active system.

[0004] A roll control system in accordance with the present inventionfor installation between axially aligned wheels of a motor vehiclecomprises a torsion bar; a damper attached to one end of the torsion barand attachable to one of the wheels; and attachment means attached tothe other end of the torsion bar and attachable to the other wheel;wherein the damper comprises an axially extending cylindrical housing; apiston slidably mounted inside the housing; a piston rod connected tothe piston, extending out of one end of the housing, and movable in anaxial direction relative to the housing; a floating piston slidablymounted in the housing between the piston and the other end of thehousing; a compensation chamber between the floating piston and theother end of the housing containing a first pressurised fluid; acompression chamber between the floating piston and the pistoncontaining a second pressurised fluid; a rebound chamber between thepiston and the one end of the housing containing the second pressurisedfluid; valve means on the piston allowing restricted flow of the secondpressurised fluid between the compression chamber and the reboundchamber; a rebound stop positioned in the rebound chamber between thepiston and the one end of the housing and providing a spring-effect onthe movement of the piston towards the one end of the housing; and acompression stop providing a spring-effect on the movement of the pistontowards the floating piston.

[0005] The present invention provides an improved passive roll controlsystem in which the passive spring of a standard torsion bar is replacedby the combined effect of a spring and damper acting together. The rollcontrol system of the present invention can be easily adapted to providea semi-active roll control system by controlling fluid flow between thecompression and rebound chambers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention will now be described, by way of example,with reference to the accompanying drawings, in which:—

[0007]FIG. 1 is a schematic view of a motor vehicle having a rollcontrol system in accordance with a first embodiment of the presentinvention;

[0008]FIG. 2 is a perspective view of the roll control system of FIG. 1;

[0009]FIG. 3 is a schematic cross-sectional view of the damper of theroll control system of FIG. 2;

[0010]FIG. 4 is a perspective view of a roll control system inaccordance with a second embodiment of the present invention;

[0011]FIG. 5 is a perspective view of the roll control system inaccordance with a third embodiment of the present invention;

[0012]FIG. 6 is a cross-sectional view of the damper of the roll controlsystem of FIG. 5;

[0013]FIG. 7 is a perspective view of the roll control system inaccordance with a fourth embodiment of the present invention;

[0014]FIG. 8 is a cross-sectional view of the damper of the roll controlsystem of FIG. 7; and

[0015]FIG. 9 is a schematic of the effect on roll control of a motorvehicle having a roll control system in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016]FIG. 1 shows an outline of a motor vehicle 10 having a pair offront wheels 12 and a pair of rear wheels 14. Each wheel 12,14 isrotatably mounted on an axle 16 and attached to the body of the motorvehicle 10 by way of a suspension unit 18. A roll control system 20 inaccordance with a first embodiment of the present invention is connectedbetween the front wheels 12. Alternatively, a substantially identicalroll control system may be connected between the rear wheels 14. As afurther alternative, substantially identical roll control systems may beconnected between the front wheels 12 and the rear wheels 14.

[0017] Referring to FIG. 2, the roll control system 20 comprises atorsion bar 22, a damper 24, and a substantially rigid arm 25. Thedamper 24 is mounted between one end 28 of the torsion bar 22 and one ofthe suspension units 18. The rigid arm 25 is mounted between the otherend 29 of the torsion bar 22 and the other suspension unit 18.

[0018] A preferred arrangement for the damper 24 is shown in FIG. 3. Thedamper 24 comprises an axially extending cylindrical housing 52 whichhas a closed first end 54, and a substantially closed second end 55. Apiston 34 makes a sealing sliding fit with the inner surface 56 of thehousing 52. A floating piston 35 makes a sealing sliding fit with theinner surface 56 of the housing 52 between the piston 34 and the closedfirst end 54. The piston 34 defines, within the housing 52, a first(compression) chamber 30 between the piston 34 and the floating piston35, and a second (rebound) chamber 32 between the piston and the secondend 55. The floating piston 35 defines, within the housing 52, a third(compensation) chamber 37 between the floating piston and the first end54. A piston rod 58 is secured to the piston 34, extends through therebound chamber 32 and out of the second end 55 of the housing 52, andis secured to one end 28 of the torsion bar 22. The first end 54 of thehousing 52 is secured to the suspension unit 18. The piston 34 andpiston rod 58 are movable together in the axial direction relative tothe housing 52. The floating piston 35 is movable in the axial directionrelative to the housing 52.

[0019] The compensation chamber 37 contains a first pressurised fluid,for example nitrogen. The compression chamber 30 and the rebound chamber32 contain a second pressurised fluid, such as hydraulic fluid. A valvearrangement 36 is mounted on the piston 34 which allows a restrictedflow of hydraulic fluid between the compression chamber 30 and therebound chamber 32. A rebound stop 60, preferably of elastomericmaterial, is mounted on the piston rod 58 inside the rebound chamber 32.A compression stop 62, preferably of elastomeric material, is mounted onthe piston rod 58 between the second end 55 of the housing 52 and a stopmember 64 secured to the piston rod. In an alternative arrangement, thecompression stop could be positioned in the compression chamber 30between the piston 34 and the floating piston 35.

[0020] The rebound stop 60 restricts axial movement of the piston 34towards the second end 55 of the housing 52 during rebound movement ofthe damper 24 by providing a spring stiffness effect on the movement.The compression stop 62 restricts axial movement of the piston 34towards the first end 54 of the housing 52 during compression movementof the damper 24 by providing a spring stiffness effect on the movement.With this arrangement, the characteristics of the torsion bar 22 arechanged from a passive spring to a spring and damper acting together, asillustrated in FIG. 9, where spring 90 is the spring stiffness effect ofthe torsion bar 22, spring 92 is the spring stiffness effect of the stop60 or 62, and damper 94 is the damping coefficient effect of the damper24. Such an arrangement improves roll damping without affecting heavedamping characteristics. The damping characteristics of the rebound stop60 and the compression stop 62 are predetermined dependent on vehiclerequirements, and can be adjusted by changing the material and/orproperties and/or shape of the stops. For example, the elastomeric stops60, 62 may be replaced by metallic coil springs, such as titaniumsprings.

[0021]FIG. 4 shows a second embodiment of roll control system 200 inaccordance with the present invention which is substantially identicalto the first embodiment, except that the rigid-arm has been replaced bya second damper 24. The two dampers 24 are substantially identical.

[0022]FIG. 5 shows a third embodiment of roll control system 20′ inaccordance with the present invention which is substantially identicalto the first embodiment. In this third embodiment, the valve arrangementof the damper 24′ has been replaced by a solenoid actuated valve 36′(FIG. 6) which is electrically connected to a control unit 26 by a line40.

[0023] The control unit 26 is preferably a microprocessor which receivessignals from one or more sensors (such as a vehicle speed sensor 42, atransmission speed sensor 44, a steering wheel angle sensor 46, and/or adriver preference switch 48) monitoring certain vehicle conditionsand/or driver preference. The control unit 26 controls the actuation ofthe valve 36′, and hence controls the flow of hydraulic fluid betweenthe compression chamber 30 and the rebound chamber 32, dependent on thesignals received from the sensors and driver preference switch, and mayalso actuate an alarm, such as a warning light 50, inside the vehicle 10during certain monitored conditions. The presence of the control unit 26and the electrically controlled valve 36′ provide the option of asemi-active roll control system in which the damping characteristics ofthe damper 24′ may be adjusted dependent on predetermined vehicleconditions.

[0024]FIG. 7 shows a fourth embodiment of roll control system 20″ inaccordance with the present invention which is substantially identicalto the first embodiment. In this fourth embodiment, the fluid in thecompression chamber 30 and the rebound chamber 32 is amagnetorheological fluid, and the valve arrangement comprises an orifice39 in the piston 34, with an associated viscosity control device 36″mounted on the piston 34 (FIG. 8). The control device 36″ creates avariable magnetic field on the fluid in the orifice 39, and iselectrically connected to a control unit 26′ by a line 40′.

[0025] The control unit 26′ is preferably a microprocessor whichreceives signals from one or more sensors (such as a vehicle speedsensor 42, a transmission speed sensor 44, a steering wheel angle sensor46, and/or a driver preference switch 48) monitoring certain vehicleconditions and/or driver preference. The control unit 26′ controls theactuation of the control device 36″, and hence controls the viscosity ofthe magnetorheological fluid as the fluid passes between the compressionchamber 30 and the rebound chamber 32, dependent on the signals receivedfrom the sensors and driver preference switch, and may also actuate analarm, such as a warning light 50, inside the vehicle 10 during certainmonitored conditions. The presence of the control unit 26′, themagnetorheological fluid, and the control device 36″ provide the optionof a semi-active roll control system in which the dampingcharacteristics of the damper 24″ may be adjusted dependent onpredetermined vehicle conditions, up to the point of locking of thedamper 24″.

[0026] Alternative arrangements for the above described embodiments forthe or each damper 24 may be used. For example, the mounting arrangementof the damper 24 may be reversed with the piston rod 58 attached to thesuspension unit 18 and the housing 52 attached to the torsion bar 22.

[0027] The present invention provides a roll control system in which thepassive spring of a standard torsion bar is replaced by a spring anddamper acting together, thereby providing an improved passive rollcontrol system. The roll control system can be easily altered to providea semi-active roll control system by controlling fluid flow between thecompression and rebound chambers.

1. A roll control system for installation between axially aligned wheelsof a motor vehicle, the roll control system comprising a torsion bar; adamper attached to one end of the torsion bar and attachable to one ofthe wheels; and attachment means attached to the other end of thetorsion bar and attachable to the other wheel; wherein the dampercomprises an axially extending cylindrical housing; a piston slidablymounted inside the housing; a piston rod connected to the piston,extending out of one end of the housing, and movable in an axialdirection relative to the housing; a floating piston slidably mounted inthe housing between the piston and the other end of the housing; acompensation chamber between the floating piston and the other end ofthe housing containing a first pressurised fluid; a compression chamberbetween the floating piston and the piston containing a secondpressurised fluid; a rebound chamber between the piston and the one endof the housing containing the second pressurised fluid; valve means onthe piston allowing restricted flow of the second pressurised fluidbetween the compression chamber and the rebound chamber; a rebound stoppositioned in the rebound chamber between the piston and the one end ofthe housing and providing a spring-effect on the movement of the pistontowards the one end of the housing; and a compression stop providing aspring-effect on the movement of the piston towards the floating piston.2. A roll control system as claimed in claim 1, wherein the compressionstop is positioned around the piston rod outside of the housing betweena stop member secured to the piston rod and the one end of the housing.3. A roll control system as claimed in claim 1, wherein the compressionstop and/or the rebound stop is formed from elastomeric material.
 4. Aroll control system as claimed in claim 1, wherein the compression stopand/or the rebound stop is a metallic spring.
 5. A roll control systemas claimed in claim 1, wherein) the first pressurised fluid is nitrogen.6. A roll control system as claimed in claim 1, wherein the secondpressurised fluid is hydraulic fluid.
 7. A roll control system asclaimed in claim 1, wherein the valve means is electronically actuated;the system further comprising an electronic control unit monitoring oneor more predetermined signals, the control unit being electricallyconnected to the valve means to control the flow of the secondpressurised fluid between the compression chamber and the reboundchamber dependent on the monitored predetermined signals.
 8. A rollcontrol system as claimed in claim 7, wherein the valve means is asolenoid valve.
 9. A roll control system as claimed in claim 1, whereinthe second pressurised fluid is a magnetorheological fluid; and whereinthe valve means is an electrically actuated viscosity control device;the system further comprising an electronic control unit monitoring oneor more predetermined signals, the control unit being electricallyconnected to the control device to control the viscosity of themagnetorheological fluid passing between the compression chamber and therebound chamber dependent on the monitored predetermined signals.
 10. Aroll control system as claimed in claim 7, wherein the control unit is amicroprocessor which is electrically connected to, and receives thepredetermined signals from, one or more sensors mountable on the vehicleand monitoring predetermined vehicle operating conditions, and/or adriver preference switch.
 11. A roll control system as claimed in claim1, wherein the attachment means comprises a second damper, the twodampers being substantially identical.
 12. A roll control system asclaimed in claim 1, wherein the attachment means is a rigid arm.
 13. Aroll control system as claimed in claim 1, wherein the piston rod of theor each damper is attached to the torsion bar.
 14. A roll control systemas claimed in claim 2, wherein the compression stop and/or the reboundstop is formed from elastomeric material.